a. Field of the Invention
The present invention relates to a microscope objective and, more particularly, to a microscope objective having a correcting means.
B. Description of the Prior Art
When manufacturing a microscope objective, adjustment of the objective is generally carried out by using a cover glass of accurate thickness which is prescribed in JIS (DIN 58884 in West Germany and ASTM Designation E211-65T in U.S.A.). For example, for the most widely used over glass which is provided in JIS R 3702, No. 1s, the standard value of thickness is prescribed as 0.17 mm. When, therefore, adjusting a microscope objective which is intended to be used with a cover glass of thickness according to JIS R 3702, No. 1s, in the course of manufacture, a cover glass having the accurate thickness of 0.17 mm is used for adjustment. On the other hand, however, thickness of cover glasses is not always 0.17 mm accurately but there is an error in the thickness to some extent. In JIS standard, the tolerable range of thickness of the above-mentioned cover glass according to JIS R 3702, No. 1s, for example, is prescribed as 0.15 mm to 0.18 mm. When a microscope objective is actually used in practice, the cover glass to be used with it becomes different from the particular cover glass which was used for adjustment in the course of manufacture. Due to the fact that individual cover glasses have considerable errors in their actual thickness as described in the above, the user has to observe an object by using a cover glass for which the thickness is different from that of the particular cover glass used for adjustment in the course of manufacture. When such cover glass having the thickness different from that of the cover glass with which the objective was adjusted is used for observation, aberrations especially spherical aberration will be aggravated and, therefore, the actual performance of the microscope objective will become inferior to its design performance. For observation in general, however, microscope objectives are used by leaving the deteriorated image as it is due to the reasons that deterioration of the image caused by variation of thickness of the cover glass is not so large and does not have serious influence on the result of observation and that the objective cannot be easily adjusted according to variation of thickness of the cover glass to be used in practice.
Recently, however, more precise observation and measuring are required in the field of medical science, especially in scientific researches in medical science, and in industrial fields. Consequently, even the above-mentioned slight deterioration of the image is not considered as a large disadvantage.